Corrosion Protection Method And Corrosion Protection Structure

ABSTRACT

A semiconductor layer ( 12 ) is caused to receive electromagnetic waves ( 1 ) to emit electrons; the emitted electrons are collected and supplied to an object to be protected against corrosion; and the electrons ( 3 ) are returned from the object to be protected against corrosion ( 16 ), to which the electrons ( 2 ) are supplied, to the semiconductor layer ( 12 ) via an electrolytic layer ( 14 ), to thereby cause an electric current to flow to the object to be protected against corrosion ( 16 ) to make a potential of the object to be protected against corrosion ( 16 ) low. In a corrosion protection structure ( 10 ), an electron supplier ( 13 ) is electrically connected to a object to be protected against corrosion ( 16 ), to thereby provide corrosion protection, the electron supplier ( 13 ) being made of a semiconductor layer ( 12 ) formed on a supporting member ( 11 ) that is capable of transmitting electromagnetic waves and has electrical conductivity. In addition, the electron supplier ( 13 ) is electrically connected to an object to be protected against corrosion ( 16 ) via an electrolytic layer ( 14 ) that is at least in contact with the semiconductor layer ( 12 ). According to the present invention, even if an object to be protected against corrosion is coated with a coating layer such as a rebar in concrete, it is possible to provide a corrosion protection method and a corrosion protection structure that can obtain a sufficient corrosion protection effect.

TECHNICAL FIELD

The present invention relates to a cathodic corrosion protection method and a corrosion protection structure thereby. More particularly, the present invention relates to a corrosion protection method and a corrosion protection structure in the case where objects to be protected against corrosion are coated with a coating layer such as rebars in the concrete.

Priority is claimed on Japanese Patent Application No. 2009-8068, filed on Jan. 16, 2009, the content of which is incorporated herein by reference.

BACKGROUND ART

There are construction techniques in which an electric current is caused to flow from an electrode (for example, an anode) installed on the surface of the concrete to steel materials such as rebars in the concrete. This changes the potential of the steel materials to a level that does not produce corrosion, to thereby prevent the progress of corrosion. Among these, electrical protection techniques are known.

In conventional electrical corrosion protection techniques, electron suppliers for use in the case where there is a need of continuously flowing an electric current outdoors include an external power source and a galvanic anode (a sacrificial anode) made of a substance whose oxidation-reduction potential is lower than that of the steel material to be electrically protected against corrosion, such as base metal, for example, zinc, magnesium, or aluminum, or made of an alloy of these.

However, the external power source has problems in that the maintenance management of power source and the management of corrosion protection current are required, and in that obtaining a commercial power source is sometimes difficult. Furthermore, the galvanic anode has a problem of being consumed over time.

To address such problems, corrosion protection methods have been proposed in recent years in which a titanium oxide coating is utilized as an electron supplier.

For example, Patent Document 1 proposes forming on a surface of stainless steel a coating that includes a titanium oxide.

Patent Document 2 asserts that a metal to be protected can be protected by injecting electrons, which are produced when light hits a titanium oxide coating provided on a base such as a metal plate or a plastic film, into the metal through an electrically conductive line.

Patent Document 3 asserts that a metal to be protected can be protected by collecting electrons, which are produced when light hits a titanium oxide coating, using a conductive coating, and injecting collected electrons into the metal.

PRIOR ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application, First     Publication No. H06-10153 -   [Patent Document 2] Japanese Unexamined Patent Application, First     Publication No. 2001-234370 -   [Patent Document 3] Japanese Unexamined Patent Application, First     Publication No. 2001-262379

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, the proposal of Patent Document 1 has a problem in that it is not possible to protect against corrosion a metal such as rebars buried in the concrete or such as steel material coated with a corrosion protection coating, for example, coating agent. It is because a coating that includes a titanium oxide is formed directly on the surface of the metal material.

On the other hand, the method and apparatus of Patent Document 2 uses an electrically conductive line. This makes it possible to inject electrons into metal such as rebars buried in concrete.

In Experiment 2 of Example in Patent Document 2, a titanium oxide film is formed on an ITO conductive glass. Therefore, it is the same in structure as the one shown in FIG. 5 of Patent Document 3. However, according to this experiment, even if a beam with a wavelength of 360 nm is irradiated with the strongest light intensity of 25 mW cm⁻² when the thickest titanium oxide film of 3 μm is used, the potential of the anode remains at −584 mV, the difference in potential from the carbon steel (−400 mV) is only 184 mV. This value is not sufficiently low compared with the typical potential of the sacrificial anode, which is −1000 mV or less.

In Patent Documents 2 and 3, the inventions are assumed to be capable of providing corrosion protection even if the coating that includes the titanium oxide as an anode is positioned in the air. However, the experiments in Example in both of the Documents are all carried out in a state with the object to be protected against corrosion and the anode being immersed in the solution of sodium chloride.

Consequently, these Examples do not prove the advantages of the inventions. As a result, the amount of the produced electrons at the anode when the anode is installed in the air is not identified, and hence, it is not clear whether the amount of produced electrons necessary for the corrosion protection is obtainable or not. Therefore, electrons sufficient for the corrosion protection may not be produced in the environment where a water film is not formed on the surface of the anode by moisture in the air or by rain.

The protection circuits shown in Patent Documents 2 and 3 have a circuit configuration having a sequence of the anode, the electrically conductive line and the object to be protected against corrosion. These circuits are not closed circuits unlike typical corrosion protection circuits in external power source systems. To continue the production of electrons at the anode in such a circuit configuration, it is required to continue the production of hydroxyl radicals (OH) by oxydizing water contained in water drop film, which is formed by raindrops or moisture in the air, as shown in FIG. 5 and FIG. 6 of Patent Document 3. However, in Patent Documents 2 and 3, no description is made about a mechanism of continuing the production of hydroxyl radicals.

In the first place, the inventors of the inventions of Patent Documents 2 and 3 are leading experts in photocatalysts in Japan. These inventions are ones to which the principles of photocatalysts are applied. Through the irradiation of light, titanium oxide produces two types of carriers: electrons (e⁻) and holes (h⁺). To obtain the self-cleaning effect of photocatalysts, an oxidation-reduction reaction by titanium oxide is utilized. The oxidation-reduction reaction consists of: an oxidation reaction in which water is oxidized by holes (h⁺) to produce hydroxyl radicals (OH); and a reduction reaction in which oxygen in the air is reduced by electrons (e⁻) to produce superoxide anions (O₂ ⁻).

Although no specific description is made in Patent Documents 2 and 3, FIG. 5 and FIG. 6 of Patent Document 3 may be regarded as schematic diagrams showing that the inventions are made of: an oxidation reaction in which hydroxyl radicals (OH) are produced; and a reduction reaction in which superoxide anions (O₂ ⁻) are produced. Therefore, in Experiment 2 in the Example of Patent Document 2 for evaluating the corrosion protection circuit shown in these figures, the corrosion protection circuit may be regarded as a circuit in which electrons flow from the anode through the electrically conductive line through the object to be protected against corrosion through the solution of sodium chloride and into the anode. In the circuit, electrolysis of water presumably allows an electric current to flow. Then, since oxygen is produced at the anode and hydrogen is produced at the object to be protected against corrosion, hydroxyl radicals and superoxide anions are presumably consumed continuously. Namely, in the circuit, a large amount of electric current flows presumably because electrolysis of water causes two types of carriers: electrons (e⁻) and holes (h⁺) to be continuously consumed.

In the inventions of Patent Documents 2 and 3, it is required that the titanium oxide not only have water attached to its surface but also be electrically connected to the object to be protected against corrosion via the solution of sodium chloride. In the inventions, unless the hydroxyl radicals and the superoxide anions are continuously consumed, a large amount of electric current does not flow. Hence, it is not possible to bring the corrosion protection potential of the object to be protected against corrosion sufficiently low.

Therefore, if the corrosion protection methods proposed in Patent Documents 2 and 3 are to be utilized, it is required that both of the object to be protected against corrosion and the anode be installed in water or in an environment in which they are exposed to water, as is the case with Examples of Patent Document 2 and 3. This leads to a problem in that the environment in which the corrosion protection structure can be installed is extremely restricted. Furthermore, another problem is posed in that it is not possible to provide a protection film when there is a need of protecting a titanium oxide layer against damage or excessive dirt.

The present invention has been achieved in view of the above circumstances, and has an object to provide a corrosion protection method and a corrosion protection structure in which a degree of freedom in installation of the corrosion protection structure is high and a sufficient corrosion protection effect is obtainable even if objects to be protected such as rebars in the concrete are covered with a coating layer.

Technical Solution

As a result of careful examinations to solve the above problems, the inventors of the present invention have obtained this knowledge. In order to inject a multitude of electrons into a corrosion protection target even if a semiconductor layer is present in the air such as in a wall of a constructed structure and will not be substantially brought into contact with water, a circuit is required to have a configuration in which electrons move from the semiconductor layer to the corrosion protection target, and then return to the semiconductor layer.

The present invention has been achieved based on the knowledge. A first embodiment of the invention is a corrosion protection method characterized which flows an electric current to an object to be protected against corrosion to make a potential of the object to be protected against corrosion low, including: emitting electrons by causing a semiconductor layer, a surface layer of which is protected so as not to be substantially brought into contact with water, to receive electromagnetic waves; collecting the emitted electrons and supplying them to an object to be protected against corrosion; and returning the electrons from the object to be protected against corrosion, to which the electrons are supplied, to the semiconductor layer via an electrolytic layer.

A second embodiment of the invention is the corrosion protection method according to the first embodiment, in which the semiconductor layer is supported by a plastic film that is capable of transmitting electromagnetic waves and has imperviousness, and the semiconductor layer is installed on the object to be protected against corrosion so that the film is a surface for receiving the electromagnetic waves, to thereby protect the semiconductor layer by the film.

A third embodiment of the invention is the corrosion protection method according to the first or second embodiment, in which in a place that is not exposed to direct sunlight, the semiconductor layer is caused to receive electromagnetic waves with a wavelength of at least 360 nm to 500 nm, to thereby emit electrons.

A fourth embodiment of the invention is the corrosion protection method according to any one of the first to third embodiments, in which an electrolytic layer having glutinousness or adhesiveness that is formed as a layer is stuck on a layer including cement into which the object to be protected against corrosion is buried.

A fifth embodiment of the invention is the corrosion protection method according to any one of the first to third embodiments, in which an electrolytic layer having glutinousness or adhesiveness that is formed as a layer is stuck on a coating of a coating agent for covering the object to be protected against corrosion.

A sixth embodiment of the invention is a corrosion protection structure characterized in that an electron supplier is electrically connected to an object to be protected against corrosion, to thereby provide corrosion protection. The corrosion protection structure includes the electron supplier made of a semiconductor layer formed on a supporting member that is capable of transmitting electromagnetic waves and has imperviousness and electrical conductivity. In the corrosion protection structure, the electron supplier is electrically connected to an object to be protected against corrosion at least via an electrolytic layer that is in contact with the semiconductor layer.

A seventh embodiment of the invention is the corrosion protection structure according to the sixth embodiment in which an electrically conductive layer is interposed between the electrolytic layer and the object to be protected against corrosion.

An eighth embodiment of the invention is the corrosion protection structure according to the seventh embodiment in which the electrically conductive layer is a layer including cement, and the object to be protected against corrosion is made of metal including iron.

A ninth embodiment of the invention is the corrosion protection structure according to any one of the sixth to eighth embodiments, in which the electrolytic layer is an agglutinant layer or an adhesive layer.

A tenth embodiment of the invention is the corrosion protection structure according to any one of the sixth to ninth embodiments, in which the supporting member is capable of transmitting electromagnetic waves with a wavelength of at least 360 nm to 500 nm.

An eleventh embodiment of the invention is the corrosion protection structure according to any one of the sixth to tenth embodiments, in which the supporting member is an impervious plastic film that has an electrically conductive thin film on a side of the semiconductor layer.

A twelfth embodiment of the invention is the corrosion protection structure according to any one of the sixth to eleventh embodiments, in which the semiconductor layer is a layer that includes one or more types of compounds selected from oxides of metals including compounds with a perovskite structure and from metal chalcogenides.

A thirteenth embodiment of the invention is the corrosion protection structure according to any one of the sixth to twelfth embodiments, in which the semiconductor layer includes a brookite-type compound.

A fourteenth embodiment of the invention is the corrosion protection structure according to any one of the sixth to thirteenth embodiments, in which the semiconductor layer is a layer including one or more types of metal oxides selected from a titanium oxide, a zinc oxide, and a tin oxide.

Effect of the Invention

According to the first embodiment of the invention, the semiconductor layer does not become wet by rain or the like, and dirt does not adhere thereto. This increases the degree of freedom for the place where the semiconductor layer is installed. In addition, a multitude of electrons can be injected into an object to be protected against corrosion, to thereby perform an effective corrosion protection treatment. Furthermore, the electrons produced by causing the semiconductor layer made of titania (titanium oxide) or the like to receive visible light can be supplied to the steel material in the concrete. As a result, the anode is not consumed, and the electrical corrosion protection is made available even in the place where it is difficult to obtain electricity by a commercial power source.

According to the second embodiment of the invention, the semiconductor layer does not become wet by rain or the like, and it is possible to prevent contamination, deterioration, and damage of the semiconductor layer. Therefore, the degree of freedom for the place where the semiconductor layer is installed is high. In the case of protecting the steel material or the like buried in the mortar or concrete against corrosion, the semiconductor layer together with the layer of the mortar or concrete over which the steel material or the like is present is also protected by the film. Therefore, it is possible to suppress the permeation of deterioration factors for mortar or concrete such as ion chloride or carbon dioxide into the mortar or concrete around the steel material or the like. This suppresses deterioration of the mortar or concrete.

According to the third embodiment of the invention, it is possible to install the semiconductor layer even in the shade, and provide the high degree of freedom in construction work for corrosion protection.

According to the fourth embodiment of the invention, it is easy to undertake corrosion protection work of the steel material buried in the mortar or concrete, and it is possible to make it possible to significantly reduce the labor required for installing the anode.

According to the fifth embodiment of the invention, even if the object to be protected against corrosion is made of metal coated with a coating layer of a coating agent, sticking the electrolytic layer having glutinousness or adhesiveness on the coating makes corrosion protection possible.

According to the sixth embodiment of the invention, the semiconductor layer does not become wet by rain or the like, and dirt does not adhere thereto. Therefore, the degree of freedom for the place where the semiconductor layer is installed is high. Furthermore, even if the amount of emitted electrons is low, an effective injection of the electrons into the object to be protected against corrosion makes it possible to perform effective corrosion protection.

According to the seventh embodiment of the invention, it is possible to protect the steel material buried in the mortar or concrete against corrosion. Furthermore, it is possible to protect a metal on which a corrosion protection coating, such as insulative coating agent, is formed against corrosion.

According to the eighth embodiment of the invention, it is possible to protect the steel material buried in the mortar or concrete against corrosion.

According to the ninth embodiment of the invention, it is easy to undertake corrosion protection work on the steel material buried in the mortar or concrete and on the metal on which a corrosion protection coating such as a coating agent is formed.

According to the tenth embodiment of the invention, it is possible to utilize typical visible light.

According to the eleventh embodiment of the invention, it is possible to prevent contamination, deterioration, and damage of the semiconductor layer.

According to the twelfth embodiment of the invention, even if incident electromagnetic waves are weak, it is possible to emit a multitude of electrons to perform effective corrosion protection.

According to the thirteenth embodiment of the invention, even if incident electromagnetic waves are weak, it is possible to emit a multitude of electrons to perform effective corrosion protection.

According to the fourteenth embodiment of the invention even if incident electromagnetic waves are weak, it is possible to emit a multitude of electrons to perform effective corrosion protection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a corrosion protection structure of Example 1.

FIG. 2 is a schematic cross-sectional view showing a test method for the corrosion protection structure of Example 1.

FIG. 3 is a schematic cross-sectional view showing a corrosion protection structure of Comparative Example 1.

FIG. 4 is a schematic cross-sectional view showing a test method for the corrosion protection structure of Comparative Example 1.

FIG. 5 is a graph showing a result of Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereunder is a description of the present invention based on embodiments, with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of a corrosion protection structure according to the present invention. A corrosion protection structure 10 shown in FIG. 1 is a corrosion protection structure that prevents corrosion in which an electron supplier 13, which is made of a semiconductor layer 12 formed on a supporting member 11 that is capable of transmitting electromagnetic waves and has imperviousness and electric conductivity, is electrically connected to an object to be protected against corrosion 16 via an electrolytic layer 14 at least in contact with a semiconductor layer 12.

Furthermore, the object to be protected against corrosion 16 and the electron supplier 13 are electrically connected to each other. As an electrically conductive layer 15, a concrete layer is interposed between the electrolytic layer 14 and the object to be protected against corrosion 16.

In the corrosion protection structure 10, the semiconductor layer 12 is caused to receive electromagnetic waves 1 to emit electrons. The emitted electrons are collected and supplied to the object to be protected against corrosion 16 via a conductor 7. From the object to be protected against corrosion 16 to which the electrons 2 are supplied, electrons 3 are returned to the semiconductor layer 12 via the electrolytic layer 14, thus causing an electric current to flow. Thereby, the potential of the object to be protected against corrosion 16 is made low.

Because the electrolytic layer 14 has a greater electric resistance than the conductor 7, the electrons 2 that are produced in the semiconductor layer 12 and collected by the supporting member 11 flow through the conductor 7, which has a less electric resistance. When the electrons having flowed through the conductor 7 reach the object to be protected against corrosion 16, the electrons 2 move from the semiconductor layer 12 to the object to be protected against corrosion 16 if the semiconductor layer 12 is lower in potential than the object to be protected against corrosion 16 or if the semiconductor layer 12 and the object to be protected against corrosion 16 are equal in potential. Furthermore, the electrons having moved to the object to be protected against corrosion 16 are transferred by the electrolyte in the electrolytic layer 14 to the semiconductor layer 12. Namely, in other words, in the present invention, the electric current produced in the semiconductor layer 12 is caused to flow to the object to be protected against corrosion 16 via the electrolytic layer 14.

Namely, in the corrosion protection structure 10 of FIG. 1, electrical connection is formed respectively between the electron supplier 13 and the conductor 7, the conductor 7 and the object to be protected against corrosion 16, the object to be protected against corrosion 16 and the concrete layer 15, the concrete layer 15 and the electrolytic layer 14, and the electrolytic layer 14 and the electron supplier 13, to thereby form a closed circuit. This returns electrons from the object to be protected against corrosion 16, to which the electrons have been supplied, to the semiconductor layer 12 via the electrolytic layer 14. Therefore, even if the amount of the produced electrons in the semiconductor layer 12 is small, an electric current efficiently flows to the object to be protected against corrosion 16. Thus, a great corrosion protection effect is obtained. Consequently, unlike the external power source system, there is no need to apply an external voltage.

It seems that a simple conductor may be used for the connection between the object to be protected against corrosion 16 and the semiconductor layer 12. However, the connection by a simple conductor does not produce a large amount of electric current. A large amount of electric current is obtained because the electrons having moved to the object to be protected against corrosion 16 are actively transferred by the electrolyte in the electrolytic layer 14, to thereby cause electric charges to be continuously transferred.

The electron supplier 13 is a member that produces electrons and supplies them to the object to be protected against corrosion 16. The electron supplier 13 is made of: the supporting member 11 that is capable of transmitting electromagnetic waves 1 and has imperviousness and conductivity; and the semiconductor layer 12 that is formed on the supporting member 11 and emits electrons through irradiation of electromagnetic waves 1. The electrons emitted from the semiconductor layer 12 are collected through electric conductivity that the supporting member 11 has. The electron supplier 13 is electrically connected to the object to be protected against corrosion 16 via the conductor 7 made of, for example, metal such as copper or aluminum. The electron supplier 13 injects the collected electrons into the object to be protected against corrosion 16.

The electron supplier 13 is installed on a location at which the electromagnetic waves are incident. Such a location may be a location directly exposed to light rays such as solar rays. In the present invention, even with a small amount of produced electrons, a high corrosion protection effect is obtained. Therefore, the electron supplier 13 may be installed in the shade. In addition, the electron supplier 13 may be installed, for example, under water or in a place intermittently exposed to water. However, because the electron supplier 13 causes an electric current to flow through the object to be protected against corrosion 16 via the electrolytic layer 14, the electron supplier 13 is preferably installed in a place substantially without water, for example, in the air on a wall surface of a constructed structure. Any place where no water is present is preferable because the electrolytic layer 14 will not swell or the electrolyte will not be eluted. In the case where the electron supplier 13 is installed in water or in a place intermittently exposed to water, it is preferable that the peripheral edge portions of the electron supplier 13 be subjected to a water-proof treatment by being sealed with pieces of resin such as fluorine-based resin or acrylic resin so as to prevent water from flowing into the semiconductor layer 12 and the electrolytic layer 14.

The electron supplier 13 used in the present invention has a comparatively thin plate-like shape or a film-like shape. Therefore, if a plurality of the electron suppliers 13 are stored or transported, they may be stacked in a form of sheets or may be taken up into a roll in a form of a long sheet. In addition, if the electron supplier 13 and the electrolytic layer 14 are integrated and taken up into a roll, installation of the electron suppliers 13 is made further simpler. Therefore, this is more preferable.

The conductor 7 may be fixed to the electron supplier 13 beforehand, or may be fixed to the electron supplier 13 at a construction site. The method of taking up the electron supplier 13 into a roll and fixing the conductor 7 to the electron supplier 13 at a construction site is preferable because it is easy to adapt to the conditions of the construction site.

The supporting member 11 is a base material for forming the semiconductor layer 12 thereon. With its electric conductivity, the supporting member 11 also functions as an electron collector for collecting the electrons emitted from the semiconductor layer 12. It is preferable that the supporting member 11 be a flat member such as a film, a sheet, or a plate (in the present specifications, these are generically referred to as a film). The supporting member 11 functions as a surface layer in the case where the electron supplier 13 is installed on a wall surface or the like of a constructed structure. As a result, the semiconductor layer 12 is not substantially brought into contact with water. Therefore, the supporting member 11 also functions as a protection layer for preventing the semiconductor layer 12 from becoming dirty, deteriorated, and damaged. Furthermore, the supporting member 11 also protects the mortar or concrete in the portion where a steel material or the like is present. This suppresses deterioration of the layer of the mortar or concrete surrounding the steel material or the like. Note that the phrase “is not substantially brought into contact with water” means that the main surface of the semiconductor layer 12 is not brought into contact with water in the liquid form, and does not mean that water in the liquid form and vapor in the gas form are also prohibited from intruding from an end face of the electron supplier 13 to be brought into contact with the semiconductor layer 12.

The material for forming the supporting member 11 is not particularly limited so long as it can transmit the electromagnetic waves 1 and has imperviousness and electric conductivity. However, in the present invention, the material that can emit electrons when the semiconductor layer 12 of titanium oxide or the like is caused to receive electromagnetic waves with a wavelength of at least 360 nm to 500 nm is preferable because it is possible to effectively use natural light. Therefore, it is preferable that the supporting member 11 be transparent. Here, the word “transparent” means high in total light transmission of visible light with a wavelength of 360 nm to 500 nm. However, so long as it is not 0, its lower limit is not particularly limited. The material can be appropriately selected according to the target to be protected against corrosion and the environment.

The preferable total light transmission of the supporting member 11 is not less than 50% at wavelengths of 360 nm to 420 nm, and not less than 70% at wavelengths of 360 nm to 500 nm. If the total light transmission is high, high degree of haze does not pose a problem, and the supporting member 11 may have a form of smoked glass. Rather, in the case of installing the electron supplier 13 on the lower surface of an elevated bridge or an elevated express highway beneath which automobiles pass, it is preferable in terms of prevention of traffic accidents that asperities as those of smoked glass be formed on the surface (free surface) of the electron supplier 13 so as to prevent reflection of beams of headlights at night. Such transparent materials include a glass plate and a plastic film. Of these, a plastic film is preferable because it is lighter than a glass plate, capable of being taken up into a roll, and excellent in resistance to shock.

The plastic film used for the supporting member 11 has electrical conductivity in order to collect electrodes emitted from the semiconductor of the semiconductor layer 12.

The plastic film with electrical conductivity may be a film made of an electrically conductive high polymer. Examples of electrically conductive high polymer include high polymers based on polyacetylene, on polypyrrole, on polythiophene, on polyphenylene, and on polyphenylene vinylene.

Furthermore, it is preferable that an electrically conductive thin film is stacked on a plastic film without electrical conductivity to impart electrical conductivity thereto because it offers wider selection of plastic films compared with plastic films with electrical conductivity. Materials for forming an electrically conductive thin film to be stacked on a plastic film include metals or metal oxides. Examples of the metals include platinum, gold, silver, aluminum, copper, nickel, chromium, and iron, and an alloy of these. Examples of the metal oxides include tin oxide, indium oxide, and compound materials of these. Of these materials for forming an electrically conductive thin film, metal oxides are preferable because of high transparency. Among these, indium tin oxide (ITO) is especially preferable because of its excellence in electrical conductivity, transparency, and chemical stability.

As for a method of stacking an electrically conductive thin film on a plastic film without electrical conductivity, a known method may be adopted. For example, a vacuum evaporation method, a sputtering method, a sol-gel process, or another method may be used.

Furthermore, in the case of stacking an electrically conductive thin film made of metal, application as a mesh-like thin film can secure transparency. Methods of stacking such a mesh-like thin film includes a method in which a silver paste is printed by the gravure method or the screen method, a method in which a metal foil is stacked and etched, and a method in which a developed silver layer is produced by the photographic process.

Resins for forming a plastic film that does not require electrical conductivity due to an electrically conductive thin film are not particularly limited so long as they can be formed into an impervious film. Because an electrically conductive film or a semiconductor layer 12 is stacked thereon, resins excellent in heat resistance, chemical resistance, and physical strength are preferable. As for heat resistance, the resins have a glass transition point of preferably not less than 100° C., more preferably not less than 120° C. Examples of such resins include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), tetra-accetylcellulose (TAC), polyester sulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PAr), polysulfone (PSF), polyetherimide (PEI), polyacetal, transparent-polyimide-based polymer, and polyether sulfone. Of these, especially PET and PEN are preferable in terms of costs and physical strength.

These plastic films are not particularly limited in thickness. So long as the imperviousness and the physical strength are satisfied, thin ones are preferable in terms of transparency and costs. Ones with a thickness in the range of 50 to 500 μm, preferably in the range of 50 to 200 μm are selected. To increase the physical strength, such a plastic film may be drawn, or a plurality of the plastic films of the same type or different types may be stacked.

Furthermore, to prevent the supporting member 11 from becoming dirty and to increase the weather resistance of the supporting member 11, a fluorine-based resin or an acryl-based resin as a protection layer may be stacked on the surface to be exposed.

The semiconductor layer 12 is a layer that receives the electromagnetic waves 1 to emit electrons. Materials for the semiconductor that forms the semiconductor layer 12 is not particularly limited so long as they can receive electromagnetic waves to emit electrons. For example, an element semiconductor such as silicon or germanium, or a so-called compound semiconductor represented by oxide of metal and metal chalcogenide (for example, a sulfide, a selenide, or the like), or a chemical compound having a perovskite structure may be used.

Examples of the oxides and the metal chalcogenides include oxide of titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, or tantalum; sulfide of cadmium, zinc, lead, silver, antimony, or bismuth; selenide of cadmium or lead; or telluride of cadmium.

Furthermore, examples of compound semiconductor include phosphide of zinc, gallium, indium, or cadmium; selenide of gallium arsenide or copper-indium; copper indium sulfide. Semiconductors are divided into the n type semiconductor, in which carriers involved in transmission are electrons, and the p type semiconductor, in which carriers are holes. In the present embodiment, it is preferable that the n type semiconductor be used.

Such n-type inorganic semiconductors include: TiO₂, TiSrO₃, ZnO, Nb₂O₃, SnO₂, WO₃, Si, CdS, CdSe, V₂O₅, ZnS, ZnSe, SnSe, KTa₃, FeS₂, PbS, InP, GaAs, CuInS₂, and CuInSe₂. Of these, preferable n-type semiconductors are titanium oxide (TiO₂), zinc oxide (ZnO), and tin oxide (SnO₂). Of the n-type semiconductors, brookite-type compounds are preferable because they are excellent in the ability to emit electrons.

Of these, titanium oxide is particularly preferable because it is excellent in the ability to receive electromagnetic waves to emit electrons. Titanium oxide may be anatase-type titanium oxide, but brookite-type titanium oxide is preferable because it is particularly excellent in the ability to receive electromagnetic waves to emit electrons. These semiconductors may be used singly or in combination of two or more types as required. Note that the anatase-type titanium oxide or the brookite-type titanium oxide are not limited to anatase or brookite as a natural mineral, but may be one artificially synthesized.

To form the semiconductor layer 12, a known method may be adopted. For example, a coating method such as gravure coating, bar coating, or screen coating may be used.

To increase the sensitivity of the semiconductor of the semiconductor layer 12, a sensitizing dye may be used. Sensitizing dyes include, for example, an organometallic complex dye, a porphyrin-based dye, a phthalocyanine-based dye, and a methine-based dye. These dyes are used with a view to expanding the wavelength region, controlling to a specified wavelength region, or the like at the time of photovoltaic power generation. These dyes may be used singly or in combination of two or more types as required.

The electrolytic layer 14 is sandwiched between the semiconductor layer 12 of the electron supplier 13 and the concrete layer 15 as an electrically conductive layer. The electrolytic layer 14 returns the electrons 3 from the steel material, which is the object to be protected against corrosion 16, to the semiconductor layer 12. Thereby, the electrolytic layer 14 causes an electric current to flow from the semiconductor layer 12 to the object to be protected against corrosion 16. It is preferable that the electrolyte that forms the electrolytic layer 14 also has a function of sticking the electron supplier 13 onto the concrete layer 15. Therefore, the electrolyte that forms the electrolytic layer 14 may be a solid electrolyte. But, it is preferable that the electrolyte be an electrically conductive, aqueous gel that includes an electrolyte (electrically conductive gel), because it can impart glutinousness and adhesiveness. In addition, the electrically conductive gel is preferable also because with its water retentivity, it prevents the situation in which a higher degree of dryness of the concrete causes an electric current to flow less. The resistivity (specific resistance) of the electrolytic layer 14 made of an electrically conductive gel is set according to the service life of the corrosion protection structure 10 and the environment of the installation site of the corrosion protection structure 10. In consideration of the stability of the application of electric power for a long period of time, 40 to 560Ω·cm is preferable, and 40 to 350Ω·cm is more preferable.

An electrically conductive gel is one in which water or an electrolyte is stably retained in a hydrophilic resin matrix, such as an aqueous gel mainly composed of agar, karaya gum, gelatin, sodium alginate, polyacrylic acid or a salt thereof, polyacrylamide, polyvinyl alcohol, polystyrene sulfonate, polyvinyl pyrrolidone, carboxymethyl cellulose or a salt thereof, or such as an aqueous gel made of hydrophilic polyurethane. Furthermore, they may be subjected to a cross-linkage treatment by use of a cross-linking agent in order to increase the internal cohesive power. The hydrophilic resin matrices may be used singly or in combination of two or more types as required. Of the hydrophilic resin matrices, polyacrylic acid or a salt thereof is preferable in consideration of stability in quality, adhesiveness, electrical conductivity, shape retaining ability, and the like.

For an electrically conductive gel, it is preferable that an aqueous gel obtained by blending glycerin, water, and an electrolyte with polyacrylic acid or a salt thereof and by subjecting an appropriate cross-linking treatment. If an electrically conductive gel is provided with polyvalent alcohol, a decrease in the water content of the electrically conductive gel can be surppressed. Therefore, it is possible to stabilize the anode potential for a long period of time and to maintain a low ground resistance. Polyvalent alcohol is preferable because the polyvalent alcohol brings not only working of retaining water content but also elasticity to the electrically conductive gel.

Furthermore, it is preferable that the water content of the electrically conductive gel be set typically to 5 to 50% by weight, preferably to approximately 10 to 30% by weight. If the water content is lower than this range, there are cases where the electrically conductive gel has less ability to return the electrons to the semiconductor layer 12 because the electrolyte has difficulty in moving. If the water content is higher than this range, there are cases where the electrically conductive gel has less shape retaining ability. In terms of adhesiveness and shape retaining ability, the polyvalent alcohols are adjusted to 5 to 70% by weight, and preferably to approximately 20 to 50% by weight.

Polyvalent alcohols used for the electrically conductive gel includes glycerin, polyethylene glycol, polypropylene alcohol, and the like. One or more types of polyvalent alcohols may be selected and used. Of these, glycerin is most suitable in terms of long-term water retentivity. If there is a need to increase the elasticity of the electrically conductive gel, the addition of a known filler such as titanium oxide, calcium carbonate, or talc is effective.

It is preferable that the electrolytic layer 14 be an agglutinant layer or an adhesive layer that includes an electrolyte or both of an electrolyte and an oxidation-reduction agent. The electrolyte may be optionally selected from among electrochemical-use supporting salts that are conventionally used as charge transport layers. Examples of such salts include halides and sulfates of alkaline metal such as KCl, NaCl, LiCl, K₂SO₄, and Na₂SO₄, and fluorides such as LiPF₆ and LiBF₄.

In the present invention, the semiconductor layer 12 of the electron supplier 13 is in contact with the electrolytic layer 14. Therefore, the electrons 3 return to the semiconductor layer 12 to cause an electric current to flow. With the inclusion of an electrolyte, the electrolytic layer 14 allows the electrons to move through. Additional inclusion of an oxidation-reduction agent in the electrolytic layer 14 makes the movement of the electrons smoother. Such oxidation-reduction agents include organic ones such as quinone-hydroquinone complexes, or inorganic ones such as S/S²⁻ or I₂/I⁻. Furthermore, metal iodides such as LiI, NaI, KI, CsI, and CaI₂, and iodine compounds, for example, quaternary ammonium compounds such as tetraalkylammonium iodide, pyridinium iodide, and imidazoline iodide are also preferably used.

As a method of forming the electrolytic layer 14, the electrolytic layer 14 may be applied directly on the concrete layer 15 or the object to be protected against corrosion 16, and may be then stuck on a surface of the semiconductor layer 12 of the electron supplier 13. However, it is preferable that the electrolytic layer 14 be previously formed as a layer on a surface of the semiconductor layer 12 of the electron supplier 13. When the electrolytic layer 14 is previously formed, a known method may be adopted. For example, the electrolytic layer 14 may be spread on a surface of the semiconductor layer 12 by a method such as gravure coating, bar coating, or screen coating. In the case of using an electrically conductive gel as the electrolytic layer 14, a sheet of the electrically conductive gel, which is previously formed as a layer, may be stuck on a surface of the semiconductor layer 12 because the electrically conductive gel has glutinousness or adhesiveness. In the case of taking up the electron supplier 13 and the electrolytic layer 14 integrally into a roll, or cutting the electrolytic layer 14 and the electron supplier 13 into sheets and putting the two types of sheets together, it is preferable that release paper be stacked on the surface of the electrolytic layer 14.

In the extremely small voids in the concrete layer, water and gel-like substance including water are said to be present. Main electrolytes included in these are said to be ions such as OH⁻, Na⁺, Ca²⁺, and K. With these electrolytes, the concrete layer can function as the electrically conductive layer 15. The water in the concrete layer is released into the air when dried, or the concrete layer absorbs water in the air when it is exposed to rain water or when the temperature changes during the day. Therefore, the concrete layer is in an absolutely dry state. As a result, the electrolytic layer 14 of the electron supplier 13 is stuck on the concrete layer 15, to make it possible to protect the concrete layer 15 against corrosion.

Furthermore, in the present invention, it is possible to interpose a coating film of a coating agent as the electrically conductive layer 15. A coating film of a coating agent is seemingly an insulative layer. However, the surface of the coating film has a multitude of cracks and fine holes, which often penetrate to the object to be protected against corrosion 16. The portions with the cracks or holes are not capable of shielding the water and air. Therefore, the object to be protected against corrosion 16 is likely to be corroded. However, no insulative material is present in the cracks and the fine holes. As a result, it is possible to flow an electric current through these portions. Therefore, the electrolytic layer 14 of the electron supplier 13 is stuck on a coating film of a coating agent to make it possible to provide corrosion protection. Corrosion protection with the interposition of a coating film of a coating agent may be performed only on the portions of the cracks or fine holes. As a result, it is permissible to protect extremely narrow areas against corrosion. Therefore, even if the amount of the electrons supplied from the electron supplier 13 is small, it is possible to provide extremely effective corrosion protection. In addition, the smaller the area or the number of the cracks or fine holes in the surface, the higher the corrosion protection effect is.

Furthermore, in the present invention, it is preferable that an electrically conductive gel be used as the electrolytic layer 14 because the electrically conductive gel intrudes into the cracks or fines holes in the surface to be in contact with or to be located extremely close to the object to be protected against corrosion.

As the object to be protected against corrosion 16, not only one that includes iron such as a steel material or a stainless steel but also one that includes nickel, titanium, copper, or zinc may be used to provide corrosion protection. In addition, it is obvious that exposed metal not covered with a concrete layer or a coating film of a coating agent can be protected against corrosion.

EXAMPLES

Hereunder is a specific description of the present invention with reference to examples.

[Corrosion Protection Structure of Example 1]

ITO was vacuum-deposited on a transparent PEN film with a thickness of 200 μm to prepare a supporting member 11 with a dimension of 50×35 mm with which electrical conductivity of a surface resistance: 10Ω/□ (square) was provided.

On the ITO-deposited surface of the PEN film, a brookite-type titanium oxide paste (C-paste manufactured by SHOWA DENKO K. K.) as a semiconductor layer 12 was applied and dried in a size of 40×25 mm to provide a titanium oxide layer 12 with a thickness of 10 μm. Thus, an electron supplier 13 was obtained.

As an object to be protected against corrosion 16, a steel material (SS400 material) with a dimension of 60 mm×70 mm×2 mm was used which had been blasted with alumina. To simulate a steel material 16 in a concrete layer 15, a cement paste was applied on the steel material 16 and a mortar plate with a size of 50 mm×50 mm×15 mm was adhered thereon, to thereby obtain a concrete layer 15. As the specifications of the mortar, a formula of mortar described in JIS R 5201 “Physical Testing Methods for Cement” was used in which the mass ratio of cement to standard sand is 1 to 3, with a water-cement ratio of 0.50. The cement used was Ordinary Portland Cement.

To the titanium oxide layer 12 of the obtained electron supplier 13, a sheet of a glutinous, electrically conductive gel with a charge transfer capability through ionic conduction of chlorine ions (“Technogel CR-S” manufactured by Sekisui Plastics Co., Ltd. with a thickness of 0.6 mm) is attached, to thereby provide an electrolytic layer 14. Then, the concrete layer 15 is stacked thereon. Thus, a multilayered product of the electron supplier 13, the concrete layer 15, and the object to be protected against corrosion 16 was fabricated.

The ITO-deposited surface of the supporting member 11 of the obtained multilayered product was electrically connected to the object to be protected against corrosion 16 via an electrically conductive line 7, to thereby fabricate a corrosion protection structure 10 schematically shown in FIG. 1.

In the present example, as shown in FIG. 2, a zero resistance ammeter (AM-02 manufactured by Toho Technical Research Co., Ltd.) 17 was provided on the electrically conductive line 7 in order to verify the movement of electrons 2 to the steel material 16 when the electron supplier 13 received light. Also a silver-silver chloride electrode (SSE) as a sticker-type reference electrode 18 was stuck on the concrete layer 15 and was electrically connected to the steel material 16 via an electrometer 19 in order to measure the potential of the steel material 16. Thereby, the corrosion protection structure 10 of Example 1 to which the measurement apparatus shown in FIG. 2 was connected was fabricated as a test piece. For all the electrically conductive lines 7, 8, and 9 for electrical connection, copper lines were used.

The zero resistance ammeter 17 was connected so as to show a positive electric current value when an electric current flows from the electron supplier 13 through the electrically conductive line 7 and into the steel material 16 as shown in FIG. 2. Therefore, in the case where the electrons 2 moves from the electron supplier 13 through the electrically conductive line 7 and into the steel material 16, an electric current flowing reversely from the steel material 16 through the electrically conductive line 7 and into the electron supplier 13 is observed to show a negative electric current value.

[Corrosion Protection Structure of Comparative Example 1]

A corrosion protection structure 20 of Comparative Example 1 schematically shown in FIG. 3 was fabricated similarly to that of Example 1, the difference being that the electron supplier 13 was spaced from the concrete layer 15 without providing the electrically conductive gel layer 14 and that the electron supplier 13 was turned upside down to arrange the semiconductor layer 12 on the upper side of the supporting member 11. Thus, a test piece of the corrosion protection structure 20 of Comparative Example 1, to which the measurement apparatus schematically shown in FIG. 4 was connected, was fabricated.

[Verification Test of Corrosion Protection Performance]

Light was irradiated onto the test pieces of Example 1 and the corrosion protection structure 20 of Comparative Example 1 to carry out a verification test of corrosion protection performance. For irradiation of light, a fluorescent lamp (1000 1×) in the room was used. In the case where measurement of an electric current was determined to be unavailable due to lack in light amount, a reflector lamp for taking pictures (5000 1×) was used to irradiate light. The test results are shown in Table 1.

TABLE 1 Potential of Spontaneous steel material Amount of Method of potential of during current change in irradiating Amount of steel material application potential light current (μA) (mV vs. SSE) (mV vs. SSE) (mV) Comparative fluorescent 0.000 +15.0 +15.0 0.0 Ex. 1 lamp 1000 lx Reflector 0.000 +15.0 +15.0 0.0 lamp Example 1 fluorescent −1.840 −81.7 −292.6 −210.9 lamp 1000 lx

[Review]

As shown in Table 1, in the test piece of Example 1, an electric current with minus 1.84 μA flows, and the potential of the steel material changed in the minus direction by 210.9 mV.

To protect metal against corrosion, it is at least necessary to change the potential of the object to be protected against corrosion 16 in the minus direction. It is indispensable for electrons to be supplied from the electron supplier 13 to the object to be protected against corrosion 16 (that is, for an electric current to flow from the object to be protected against corrosion 16 to the electron supplier 13).

In the test piece of Example 1, an electric current flowed, and also the potential of the steel material changed in the minus direction. As a result, it was verified that the amount of the moving electrons necessary for changing the potential of the metal was sufficient. Hence, protection of metal against corrosion is possible.

On the other hand, in the test piece of Comparative Example 1, no electric current was measured even though light was irradiated by a fluorescent lamp. Therefore, light was irradiated by a reflector lamp. However, no electric current was measured similarly to the case of the fluorescent lamp. As proof of no electric current flowing, it was verified that the potential of the steel material 16 also did not change. The test piece of Comparative Example 1 is one that corresponds to a corrosion protection method and a protection apparatus described in Patent Documents 2 and 3. Patent Documents 2 and 3 also has a description that the potential of the metal is made lower than its oxidation potential. However, in the corrosion protection structure of Comparative Example 1, even though electrons are produced in the semiconductor layer 12, almost no electric current was measured and no potential change was detected. Therefore, in environments where the test piece is not substantially brought into contact with water, the test piece of Comparative Example 1 suffers from an overwhelming shortage in the amount of moving electrons for changing the potential of metal. Therefore, the test piece is not presumably capable of protecting metal against corrosion.

[Corrosion Protection Structure of Examples 2 and 3]

ITO was vacuum-deposited on PEN films similar to Example 1, and two types of ITO-deposited PEN films with a surface resistance of 10Ω/□ and 300Ω/□ with a size of 12 cm×12 cm were used as a supporting member 11 of Examples 2 and 3.

On the ITO-deposited surface of each of the two types of supporting member 11, titanium oxide similar to Example 1 was applied and dried in a size of 10 cm×10 cm to provide a titanium oxide layer 12 with a thickness of 10 μm. Thus, electron suppliers 13 of Examples 2 and 3 were obtained.

As an object to be protected against corrosion 16, rebars (length: 25 cm, diameter: 6 mm) were used. The rebars were arranged in a grid in which six rows and six columns of rebars are evenly spaced so as to form a central layer of the concrete layer 15 in a 6-cm-thick square with an edge of 30 cm. Then, a copper line coated with a resin was attached thereto. The line was drawn out as a lead line and buried. As a surface treatment, cleaning (substrate surface conditioning) by a diamond cup was performed on a surface of the concrete substrate with the rebars. This was used as a concrete layer 15.

On the titanium oxide layer 12 of each of the obtained electron suppliers 13, a sheet of an electrically conductive gel with a size of 10 cm×10 cm similar to that of Example 1 was stuck to provide an electrolytic layer 14. The concrete layer 15 was stacked thereon to fabricate a multilayered product of the electron supplier 13, the concrete layer 15, and the object to be protected against corrosion 16. Thereby, corrosion protection structures 10 of Examples 2 and 3 as schematically shown in FIG. 1 were fabricated.

The corrosion protection structures 10 of Examples 2 and 3 to which the measurement apparatus schematically shown in FIG. 2 was connected were fabricated as test pieces, the difference being that the ITO-deposited surface of the supporting member 11 of the corrosion protection structure 10 of each of Examples 2 and 3 was electrically connected to the object to be protected against corrosion 16 via an electrically conductive line 7 made of an aluminum tape with a width of 5 mm

[Verification Test of Corrosion Protection Performance]

The test pieces of Examples 2 and 3 were installed outdoors, and generated electric currents were measured.

When each electron supplier 13 was installed outdoors, a fluorine-based resin film was cut into a ribbon shape and was stuck to the surface of the concrete layer 15 so as to cover the four edges of the supporting member 11. This was done to prevent the end faces of each electrically conductive gel layer 14 from becoming dry and swollen.

With a plurality of transparent acrylic cylinders (height: 8 cm) as supports, the test pieces of Examples 2 and 3 were installed on the floor of the roof of a building that is not exposed to light at night so that the electron supplier 13 faces downwardly while being suspended in the air. The reason for installing the electron suppliers 13 in this manner is to prevent the electron suppliers 13 from receiving direct sunlight.

The generated electric currents were measured at a frequency of once in every 60 minutes by use of small data loggers.

The measurement results are shown in FIG. 5. Exposure days in the axis of abscissas have its starting point at noon of the day when the measurement began. Therefore, the positions of the scale lines on the axis of abscissas represent noon.

The absolute values of the generated electric currents on each measurement day had a tendency to be maximum approximately at noon (at 12 AM).

In the test piece of Example 3 whose supporting member 11 had a surface resistance of 300Ω/□, an electric current was generated, from the first light of the dawn, from the start of exposure. On the other hand, in the test piece of Example 2 whose supporting member 11 had a surface resistance of 10Ω/□, almost no electric current was generated until the 20th day after the start of exposure. However, after about the 20th day from the start of exposure, an electric current began to be generated. There were approximately 11 days when an electric current larger than that of the test piece of Example 3 was generated.

What is notable is, it was observed that an electric current flowed even at night when the test pieces were not exposed to light. In the test piece of Example 2, there were times when no or extremely little corrosion current flowed at the beginning of exposure. However, with the continued application of electric current, a corrosion protection current ceased to reach zero even at night, and a corrosion protection current began to be generated from about the 20th day after the start of exposure. In the test piece of Example 3, a corrosion protection current began to clearly flow even at night after about the 9th day after the start of exposure.

In addition, surprisingly enough, once a corrosion protection current began to flow at night, an electric current which is generated by the electrons in the period of daylight hours is allowed to flow equal to or higher than an electric current value to which the electric current value at night is added.

This phenomenon happens presumably because the potential of the semiconductor layer 12 remains lower than that of the rebars since it does not become high immediately when the light amount reduces or vanishes. The reason for this is not certain, but can be assumed as follows. Although the concrete layer 15 is electrically conductive, but has a tremendously high resistance value. Therefore, a combination having a sequence of the electrically conductive gel layer 14, the concrete layer 15 and the steel material 16 has a function of a type of capacitor. Due to this and the relationship between the oxygen concentration and the ions in the electrolytic layer 14, the change in potential of the semiconductor layer 12 becomes slow. This causes the semiconductor layer 12 to fail to have a high potential originally expected to be shown in a dark place. As a result, the electric current flowing at night continues to flow in the period of daylight hours. To this, an electric current by newly generated electrons in the period of daylight hours is added.

From these, with a formation of a closed electric circuit having a sequence of the semiconductor layer 12, the ITO electron collector, the aluminum tape, the rebars, the concrete layer 15, the electrically conductive gel layer 14 and the semiconductor layer 12, an electric current by electrons generated in the period of daylight hours persistently flows at night as well without using an external power source. Therefore, a corrosion protection effect is presumably maintained. Even in the case where the supports for the test piece have electrical conductivity, the electric current flows through where it can flow with least resistance if the electron supplier 13 is not in contact with the floor surface. Therefore, it never happens that the electric current leaks out of the aforementioned closed electric circuit.

[Potential Measurement Test of Semiconductor Layer 12]

To measure the potential of the semiconductor layer 12, three sheets of electron supplier 13 were fabricated similarly to that of Example 1, the difference being that the PEN film had a dimension of 30 mm×35 mm and that the spread range of the titanium oxide had a size of 30 mm×25 mm.

To measure the potential, a sticker-type silver-silver chloride electrode (SSE) as a reference electrode 18 was stuck on the semiconductor layer 12 of each electron supplier 13, and the potentials of the three semiconductor layers 12 were measured when illumination was changed from 0 with 1000-1× pitches. The potential of the semiconductor layer 12 was measured with an electrometer. The adjustment of illumination was made with a blackout curtain, a fluorescent lamp, and a reflector lamp.

The results of the above are listed in Table 2.

TABLE 2 Potential of semiconductor layer Illumination (mV vs. SSE) (lx) Average No. 1 No. 2 No. 3 Remarks 0 −29 −17 −11 −60 Blackout curtain used 1000 −238 −247 −247 −221 Fluorescent lamp used 2000 −571 −566 −577 −571 Reflector lamp used 3000 −630 −626 −634 −630 4000 −693 −692 −696 −692 5000 −706 −710 −704 −703

As shown in Table 2, the potentials of the semiconductor layers 12 in a dark place were −11 to −60 my, the average being −29 mV. On the other hand, the spontaneous potential of the steel materials 16 were, as shown in Table 1, +15 mV in Comparative Example 1, and −81.7 mV in Example 1. Thus, in the dark place, there are cases where the steel material 16 has a minus potential, which is lower than the potential of the semiconductor layer 12. The potential of steel materials changes according to the corrosion state thereof. It is known that the heavier the corrosion is, the lower potential the steel materials show. For example, in seawater, steel materials show a potential of −454 mV to −654 mV. If a steel material indicative of such a low potential is used as an object to be protected against corrosion, the potential of the semiconductor layer 12 is inevitably high in a dark place. Therefore, it is believed that the steel material is not capable of providing corrosion protection. Rather, it was found that in the initial stage of corrosion protection, a corrosion current might be flowed by the semiconductor layer 12. However, the irradiation of electromagnetic waves with 4000 1× or greater makes the semiconductor layer 12 lower in potential. Even in such a case, corrosion protection is achieved. Furthermore, as shown in Examples 2 and 3, once electromagnetic waves are irradiated onto the electron supplier 13, the electron supplier 13 becomes lower in potential, which achieves corrosion protection. Application of an electric current for a long period of time causes a corrosion protection current to flow continuously even at night. Therefore, in the present invention, it can be said that an instantaneous flow of a corrosion current in the initial stage in a dark place does not pose a problem.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, the corrosion protection structure has a high degree of freedom in installation. Even if the object to be protected against corrosion is one coated with a coating layer such as a rebar in the concrete, it is possible to provide a corrosion protection method and a corrosion protection structure that are capable of obtaining a sufficient corrosion protection effect.

DESCRIPTION OF THE REFERENCE SYMBOLS

1: electromagnetic wave, 2: electron supplied to object to be protected against corrosion, 3: electron returned to semiconductor layer, 7, 8, 9: conductor (conductive line), 10, 20: corrosion protection structure; 11: supporting member, 12: semiconductor layer (titanium oxide layer), 13: electron supplier, 14: electrolytic layer (electrically conductive gel layer), 15: electrically conductive layer (concrete layer), 16: object to be protected against corrosion (steel material), 17: zero resistance ammeter, 18: reference electrode, 19: electrometer 

1. A corrosion protection method which flows an electric current to an object to be protected against corrosion to make a potential of the object to be protected against corrosion low, comprising: emitting electrons by causing a semiconductor layer, a surface layer of which is protected so as not to be substantially brought into contact with water, to receive electromagnetic waves; collecting the emitted electrons and supplying them to the object to be protected against corrosion; and returning the electrons from the object to be protected against corrosion, to which the electrons are supplied, to the semiconductor layer via an electrolytic layer.
 2. The corrosion protection method according to claim 1, wherein the semiconductor layer is supported by a plastic film that is capable of transmitting electromagnetic waves and has imperviousness, and the semiconductor layer is installed on the object to be protected against corrosion so that the film is a surface for receiving the electromagnetic waves, to thereby protect the semiconductor layer by the film.
 3. The corrosion protection method according to claim 1, wherein in a place that is not exposed to direct sunlight, the semiconductor layer is caused to receive electromagnetic waves with a wavelength of at least 360 nm to 500 nm, to thereby emit electrons.
 4. The corrosion protection method according to claim 1, wherein an electrolytic layer having glutinousness or adhesiveness that is formed as a layer is stuck on a layer including cement into which the object to be protected against corrosion is buried.
 5. The corrosion protection method according to claim 1, wherein an electrolytic layer having glutinousness or adhesiveness that is formed as a layer is stuck on a coating layer of a coating agent for covering the object to be protected against corrosion.
 6. A corrosion protection structure in which an electron supplier is electrically connected to an object to be protected against corrosion, to thereby provide corrosion protection, comprising: the electron supplier made of a semiconductor layer formed on a supporting member that is capable of transmitting electromagnetic waves and has imperviousness and electrical conductivity; wherein the electron supplier is electrically connected to an object to be protected against corrosion at least via an electrolytic layer that is in contact with the semiconductor layer.
 7. The corrosion protection structure according to claim 6, wherein an electrically conductive layer is interposed between the electrolytic layer and the object to be protected against corrosion.
 8. The corrosion protection structure according to claim 7, wherein the electrically conductive layer is a layer including cement, and the object to be protected against corrosion is made of metal including iron.
 9. The corrosion protection structure according to claim 6, wherein the electrolytic layer is an agglutinant layer or an adhesive layer.
 10. The corrosion protection structure according to claim 6, wherein the supporting member is capable of transmitting electromagnetic waves with a wavelength of at least 360 nm to 500 nm.
 11. The corrosion protection structure according to claim 6, wherein the supporting member is an impervious plastic film that has an electrically conductive thin film on a side of the semiconductor layer.
 12. The corrosion protection structure according to claim 6, wherein the semiconductor layer is a layer that includes one or more types of compounds selected from oxides of metals including compounds with a perovskite structure and from metal chalcogenides.
 13. The corrosion protection structure according to claim 6, wherein the semiconductor layer includes a brookite-type compound.
 14. The corrosion protection structure according to claim 6, wherein the semiconductor layer is a layer including one or more types of metal oxides selected from a titanium oxide, a zinc oxide, and a tin oxide. 